I recently e-mailed Disney for details on using Magical Express with the same question. Their reply is below. Please note that reservations must be made 10 days prior to use date, and the part about "participating" airlines. We're traveling on Northwest, and they don't participate.
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Beginning May 5, 2005, guests of Disney hotels* using Disney's Magical Express service can check their bags at their hometown airport, bypass baggage claim at Orlando International Airport (OIA) and board state-of-the-art motor coaches to the Walt Disney World Resort as their bags "magically" appear in their room upon check in. The round-trip service, which is available and complimentary during Disney's Happiest Celebration on Earth event (which also begins May 5, 2005), is designed to give Disney hotel guests the stress-free vacation they want.
How Disney's Magical Express service works
Disney's Magical Express must be booked at least 10 days prior to arrival through disneyworld.com, Disney Reservation Center by calling 407-W-DISNEY (407-934-7639) or a
travel agent beginning Jan. 2, 2005. The service commences May 5, 2005.
Guests check their specially-tagged luggage at their departure airport.
Upon arrival in Orlando, guests bypass airport baggage claim and go directly to the Disney Airport Welcome Center. Guests board state-of-the-art motor coaches that take them to their Disney hotel.
A team of Disney representatives at the airport will pick up guests' luggage and transport it to their hotel room.
Disney's Magical Express service makes guests' return to OIA hassle-free as well. This convenient system lets guests flying with participating airlines avoid airport check-in lines by enabling passengers on domestic flights to check their luggage and receive a boarding pass before ever
departing their Disney hotel. As an added benefit, guests with flight departures later in the day no longer have to worry about their luggage after they check out of their hotel. They can simply check their luggage at the Resort Airline Check-in Desk and then enjoy the last day of their stay.
* This service is offered at on-property Disney Resorts for guests departing from Orlando International Airport, with the exception of the Walt Disney World Swan and Dolphin, Shades of Green and Downtown Disney Resorts. This service is not available for guests arriving to other Central Florida airports. If you move to an off-property resort, such as Disney's Hilton Head or Vero Beach Resorts, you will need to arrange for your own transportation back to the airport.